Electric circuit control



May l2, 1942.

J. H. cANNoN ELECTRIC CIRCUIT CONTROL A Troia/VE ns May 12.- 1942 J. H. CANNON C 2,282,454

ELECTRIC CIRCUIT CONTROL Filed Aug. 2, 1940 2 sheets-sheet 2 91 @o 42 z2 J /N VENTO/Q, JA Mes H. CA /v/vo/v A TTORJNEKS @y Y HAR/P s l HAR/Ms am' M lOR THE FIRM Patented May 12, 1.942

2,282,454 ELECTRIC CIRCUIT CONTROL James H. Cannon, Los Angeles, Calif. Application August2, 1940, Serial No.y 350,012 s Claims. .torno-17) My invention relates to means for controlling -electric circuits with special reference to control systems that include limit switches for stopping electrically driven devices.

While my invention is applicable widely to cony' trol systems and may be used for diverse purposes in such systems, it is being initially em- `bodied in a system for controlling electricallyactuated landing gears for aircraft. Itis deemed I i Vsufficient for the purpose of disclosure and illustration to limit the present description to such an embodiment, since those skilledin the art will find adequate guidance therein for applying the invention wherever it may have utility.

The general object of my invention is to provide anv effective and reliable circuitI control to meet 'the exacting requirements of systems for actuating landing gears and of other systems presenting similar problems.

I Control systems of the character to which the present invention pertains are characterized by the employment of a limit switch to open a motor circuit when a driven member reaches a limit position. One of the problems commonlyencountered in such systems arises from the fact Athat a tendency for the driven member to retreat Vfrom a limit position may result in frequent closing of the limit switch. For example, in a system for the remote control of aircraft landing gear in which the landing gear is retracted in opposition to gravity, the landing gear tends to creep downward from retracted position and Vif the limit switch is sensitive the tendency may cause ,chattering, the limit switch remaining open only momentarily after each automatic energization .of the motor circuit to check the creepage. One object of my invention is to provide a control arrangement in which repeated energization of thel motor circuit to combat such creepage is relatively infrequent.

Other objects of my invention pertain specifically to the construction of a limit switch and associated elements in such a control system. One object here is to provide an'eicient form of switch to operate with snap-action. Another object is to provide a limit switch that not only operates with a snap-action, but will also operate with delayed action, at least in its closing movement, i

whereby substantial initial movement of a driven member away from the limit position may occur without causing the limit switch to close.

Other `objects and advantages of the preferred form of my invention, especially with reference to the specific structure of the limit switch, will be understood from the following description considered with the accompanying drawings.

In the drawings, which are to be taken as illustrative only:

. Fig. 1 is a schematic presentation of a preferred form of my invention, including a wiring diagram;vv

Fig. 2 is a longitudinal section through a portion of a casing and mechanism therein employed K in the preferred form of my invention, the casing cover being removed; f

Fig. 3 is a plan view of the structure shown in Fig. 2;

Figs. 4, 5, and 6 are transverse sections-taken as indicated by theA lines 4 4, 5 5, and 6-.6 of Fig. 2;

Fig. 7 is a 3 showing the initial stage of the opening action of a limit switch as the landing gear approaches one of its alternate limit positions;

i Fig. a is a simuar View showing the completion of the opening action of thelimit switch begun in Fig. 7; and 4 Fig. 9 is a similar view showing the initial stage of the closing action of the limit switch as the driven member moves away from one of its limit positions. Y

Fig. 1 indicates diagrammatically the structure of` one type `of retractable landing gear for an aircraft. Each of the landing wheels 2|lis car-'- ried by a leg 2| that. is pivotally mounted on a frame member 22 of the aircraft by a suitable bracket 23. A link 25 extending diagonally upward from the leg 2|' is pivotally connected by a pivot pin 2B to a second link 21, and the second link is in turn anchored tothe aircraft structure by a fixed pivot pin 28. The leg 2| is swung v between the retracted position shown in full lines 4t and the extended position shown ondotted lines, which positions may be 'referred to as the alternate positionsV of a driven member, Vthe driven member being the leg 2|. Y tween the twov limit positions, are, actuated through an extensible' arm generally designated 30 that is free to swing about the axisof a countershaft 3|, the extensible arm'including Yajtubular section 32 and a screw` sectionv 3'3 threaded into the tubular section. The screw section '33 is rotated by the counter-shaft 3| through suitable bevel gears thatldo not appear in the drawings.

A motor` generally desigr'iatedl 35 for actuating the landing gear of .the aircraft has a'motor shaft 56 extending in opposite.. directions from the motor; to voperate the lcountershaft 3| on one side of the aircraft and a corresponding countershaft plan View of selected elements Fig.-

'I'he ymovements be- (not shown) on the other side of the aircraft, the operative connection between the drive shaft and each of the counter shafts being provided by suitable bevel gears 31.

In the type of control arrangement to which the present invention pertains, a limit switch is provided for response to the driven member to deenergize the actuating motor as the driven member approaches a limit position, and in the instant control arrangement two such limit switches are employed. In Fig. 1 a limit switch generally designated 48 is mechanically opened as the landing gear reaches retracted disposition and a second limit switch generally designated 4| is adapted to open as the landinggear approaches fully extended disposition for landing." Any suitable arrangement may be devised to makethe limit switches responsive to the. landing gear mechanism. In the present constructionl provide a special switch-control member 42 with two switch-operating pins 43 and45 and provide for driving the switch control-member synchronously with the land gear. The means for actuating the switch control member 42 synchronously with the landing mechanism may includela'worm 41 at the switch control member,A a countershaft 48 for driving the worm 41, and a worm gear 50 on the motor shaft 36 meshing with a second worm (not shown) on the countershaft 48.V

Instead of placing such limit switches directly in the energizing circuit of the motor 35, I prefer to arrange the two limit switches in auxiliary or control circuits that govern thev motor circuit through relays. In Fig. 1 -a master switch generally designated 5| for `the control circuits is movable between alternate positions representing the alternate dispositions of the landing gear and is operated `by a control'member (not shown) within reach of the aircraft pilot; the pilot shifting the control member from one alternate position to the other whenever hel desires to `change the disposition of the landing gear.

The control circuit that-is broken by the limit switch 40 to stop the retraction movement of the landingvr gear-may be traced as follows: `battery 52, wire 53,- switch arm 55 and Contact 56 ofithe master switch 5|, wire 51, the coil of a relay`58, wire 60, limit switch 40, wire 6| to ground, and wire 62 from ground to the second'terminal of the vbattery 52. The other control' circuit, which is broken by -the limit'switch 4| to stop the extension operation of" the landing gear, mayfbe traced as follows: battery 52, wire 53,' switch arm'55 and `contact 65 of the master Vswitch 5|, wire 66, the coil of a relay 61', wire'68, limit switch 4|, wire 10 to ground and wire 62 from ground to the other side ofjthe battery 52.

`When-`the relay 58 is energized and thereby moves a pair of normally openl contact arms 1| and 12 to closed positions, a motor circuit to operate the motor 35in one rotary direction is established as follows: motor battery'13, wire 15, contact arm 1|, wire 16, wire 11,'elds coils 18 of the motor'35, wire 80, contact arm 12, wire 8|, armature contact'82, armature coils of the V motor (not shown), armature contact 83, and wire 85 to the second terminal of the motor battery 13. When the relay 61 is energized to move a pair of Y normally open contact arms 86 Vand 81 to closed positions, the motor isdriven in the opposite rotary direction by virtue ofthe following circuit: motor battery' 13, wire 15, contact arm 86, wire 88,wire 88, field-'coil 18, wire 11, contact arm 851, wire 8|, the Varmature coils `of the motor,

5 the face'of the switch and wire to the second terminal of the motor battery 13.

The manner in which the various circuits are functionally interrelated will be readily recognized. Fig. 1 shows the various parts as disposed when the landing gear is fully retracted, the switch arm 55 of the master switch 5| then being swung to the contact 56 representing the retracted disposition of the landing gear. If the pilot desires to extend the landing gear, he merely causes the switch arm 55 of the master` switch 5| to be swung to the alternate position against the contact 65 which results in energization of the relay 61, since the relay switch 4| in the corresponding control circuit is closed. Energization ofthe relay 61 moves the contact arms 86 and 81 from their normally open positions to closed positions, and the motor is thereby energized to lower the landing gear and continues to be energized until the limit switch 4| opens in response to the approach of the landing gear to the limit of its extension.` Subsequent retractionV of the landinggearl is accomplished by returning the switch- 'arm 55 of the'master switch 5| to the position against the contact 56 whereupon the relayY 58 is energized since the limit switch 40 is automatically closedV when the landing gear is extended. c

In the described landing gear, it is apparent that each of the legs 2| is swung upward into retracted position against gravity and that gravity tends to cause the landing gear to creep out of fully retracted disposition. vOne of the objects of the present invention is to prevent the motor 35 from being energized frequently, and this object is attained by designing at least the limit switch 40 for delayed action in its closing movement. Preferably -both of the limit switches 40 and 4| are of the same construction, both operating with snap action as well as delayed action in their opening and closing movement. My preferred construction for such limit switches is shown in specific detaily in Figs. 2 to 9, which construction willnow be described.

. Figs. 2 and-3 show a casing 95 having a lcompartment 9| for the switch-control member 42, a

compartment 92 for the limit switches 48 and 4|, 4and other compartments that need not be described provided to house the coils and contact arms of the two relaysV 58 and 61.

The Ypreviously Vmentioned worm 41, which is driven by the countershaft 48, is journaled in a vpair o'f bearings 93 in the compartment 9| and meshes with a worm gear 95 'keyed to a stub shaft I96. 'Ihe vstub shaft 96 is journaled in .a suitable-bearing 91 inthe compartment '9| and carries the-previously mentioned rotary switchcontrol member 42,v which member is in the form of "a `disc attached to the stub shaft by a cross pi'n 98. I

The rotary switch-control member 42 has an arcuate Vgroove |08 formed with overhanging sides to slidingly engagethe heads of two screws- |02, and the arcuate groove is cut away as indicated at |83 for admitting the heads of the screws. The previously mentioned switch operating pins 43 and 45 are vtubular members that thread onto the screws |02 for pressure against control member 42 and may lbe .provided with slots |85 in their ends for engagement bya screwdriver whenever it is desirable toA change the' 'positions lof the switch operating pins along the'arcuate groove |80.

' In the preferred form of my invention the structures ofthe two limit switches 48and 4 are identical. The principal parts of the limit switch- 40 are a switch arm |06, a first movable or rotary means |01 for direct operation of the switch arm, and a second movable or rotary means |08 for operating the first means with delayed action in response to movements of the rotary switch control member 42.

lThe switch arm |06 is in the form of a leaf spring carrying a movable contact which the leaf spring tends to hold against a cooperative stationary contact I. The switch arm |06 is carried by a small metal bracket ||2 that is electrically connected to the grounded wire 6| of the previously described wiring diagram. The stationary contact is mounted on a small metal bracket ||3 that is electrically connected with the previously mentioned wire 60 of the wiring diagram. The various parts of the two limit switches 40 and 4|, including the metal brackets ||2 and ||3, are mounted on an insulating base plate ||5 that forms a wall of the compart ment 92.

The first rotary member |01 may be in the form of a metal plate mounted on a flanged pivot member H6, the plate being cut to form a stop shoulder ||1 (Fig. 8) and a stop shoulder ||8 (Fig. '1) and being bent to form an arcuate flange |20 and a latch flange |2|. In the closed-circuit position of the rotary member |01 the flexible switch arm |06 is permitted to hold the movable contact ||0 against the` stationary contact as shown in Fig. 3, but in the open-circuit position of the rotary member |01`the arcuate flange |20 flexes the switch arm |06 to separate the contacts ||0 and ||I.

The function of the second rotary member |08 is to transmit actuating force to the first rotary member |01 in a yielding manner in response to.

the switch-control member 42, but to block the movement of the first rotary member |01 fora substantial delay period during initial stages of both circuit-closing and circuit-opening switch operations. In my preferred construction the second rotary member |08 comprises a switch finger |22 for cooperation with therotary switch control member 42 and, unitary with the finger, a latch arm |23 that is bent towardsvv the Afirst rotary member |01 to form a latch finger |25 for cooperation with the latch flange |2|. The switch nger |22, which carries the latch arm |23, is pivotally mounted on a suitable stud |26 mounted on the base plate ||5 and held thereon by a removable plate |21, the removable plate |21 being common to both limit switches 40 and 4 I.

The circuit-closing position of the second rotary member |08 is determined by a stop shoulder |28 presented by an angular plate |29, and the rotary member is continuously urged towards itcircuit-closing position by a relatively heavy laminated spring |30 that is anchored at one end by screws |3| (Figs. 2 and 4) to the base of the switch finger |22 and is suitably restrained at the other end. In the particular construction shown, I interconnect the outer end of the laminated spring |35 of the limit switch 40 and the outer end of the corresponding laminated spring |308 of the limit switch 4|, for example by a machine screw |32, so that the resistance to flexure of one of the laminated springs is reinforced by the resistanceof the other.V

To provide the required yielding connection for transmitting actuating force from the second rotary member |08 tothe first rotary member |01, I may employ a leaf spring |33 adjacent the laminated spring |30 on the base of the switch `in the arcuate flange |20.

finger |22 disposed to press against the arcuate flange |20, and I may mount a double leaf spring |34 on the other side of theswitch finger base to engage the rotary member |01 in a slot |35 cut When the second rotary member |08 is in the circuit-closing position shown in Fig. 3, the double leaf spring |34 urges the first rotary member |01 clockwise t0- wards a circuit-closing position determined byabutment of the previously mentioned stop:- shoulder ||1 of the first rotary member against; a stop block |36. The stop block |36 is common to both limiting switches 40 and 4|. When the:v second rotary member |08 is in its circuit-opening position, the leaf spring |33 as well as the doubleV leaf spring |34 tends to rotate the first rotary member |01 counter-clockwise, the tendency being to swing the stop shoulder, ||8 of the first rotary member against the stop block |36.

The movements of the first rotary member |01 in either direction to follow corresponding move- `ments of the second rotary member |08 are delayed by temporary engagements of the latch finger |25 with the latch flange |2|, as will be readily understood from the following sequence of operations. Y Let it be assumed that in Fig. 3 the switch control member 42 is being rotated clockwise as'the motor 35 is retracting the landingV gear of the aircraft. It will be noted that all the movable parts of both the limit switches 40 and 4| are in circuit-closing positions. Eventually Vthe switchoperating pin 43 moves into contact with the switch nger |22 and thereby rotates the second rotary member |08, but the resultant ilexure of the springs |30, |33, and |34 doesnot cause corresponding rotation of the first rotary member |01 because, as indicated in Fig. '1, the latch finger |25 moves into the path of the latch flange |2| before the springs are flexed to an effectiveV degree. The first stage of the circuit-opening operation of the limit switch terminates when the latch finger |25 swings clear of the latch flange |2|, permitting the latch flange to escape, whereupon the first rotary member |01 moves to the circuit-closing position shown in Fig. '1 at which position the flexible switch arm |06 is deflected to separate the contacts ||0 and With the various parts disposed as shown in Fig. '1, let it be assumed that the pilot causes the masterrswitch 5| to be swung to a position for energizing the motor 35 in the opposite direction to lower the landing gear. Immediately the synchronized switch-operating member 42 will rotate counter-clockwise to cause the switch operating pin 43 to retreat from the limit position of Fig. '1. During the first stage of the circuit-- closing operation of the limit'swit'ch 40, the rela-- tively heavy laminated springs |30 and |30a co-I operate to rotate the second rotary member |00t towards circuit-closing position, the switch finger |22 being caused to follow the retreating movement of the pin 43. The clockwise rotation of the second rotary member |08 towards circuitclosing position causes the double leaf spring |33 to flex and press the first rotary member 01 towards circuit-closing position, but the tendency of the first rotary member to follow the rotation `the latch finger |25 acting as a temporary stop for the latch flange |2|, and it will be noted that engagement of the latch finger with the latch lswitch-operating pin 43 shown in Fig. 7 with the subsequent position of the pin near the end of the rst stage of circuit-closing operation indicated in Fig. 9, it is apparent that substantial creepage of the landing gear from its extremeretracted disposition may occur without causing energ'ization of the motor circuit to maintain the retracted disposition ot the landing gear. As a result V'of the described arrangement, the landing gear is eiectively maintained in retracted disposition with only infrequentmotor operation.

Since thel second limit switch 4I is closely similar to the first limit switch 40, as indicated by corresponding numbers designatingcorresponding parts in the drawings,`it is not Vnecessary to givel any further detailed description. It will be apparent that the pin 45 cooperates with the switch nger |22gt in the same manner that the pin 43 cooperates with the switch finger |22,'the movement of the pin 45 towards the switch finger |22EL causing the limit switch 4l to open and the opposite movement of the pin 45 causing the limit switch 4| to close.

My detailed and specific description of the preferred form of my invention for a specific use will suggest to those skilled in the art various changes and substitutions in applying the underlying concept, and I reserve the right to all such changes and substitutions that properly come within the scope of my appended claims.`

-I claim as my invention: l. A limit switch of the character setforth for controlling an electrically-actuated memberata limit position of the member, said switch comprising: a pair of switch contacts; a iirst means operatively connected with said pair of contacts,

said means being movable in one direction to,A

cause said contacts to separate and in the opposite direction to cause the contacts to close together; a second means movable between a circuit-closing position and circuit-opening position, said second means being mechanically responsive to said electrically-actuated member'to move to circuit-opening position when said member approaches said limit position and to move to circuit-closing position as said member initially retreats from said limit position; means yieldingly connecting said second means with said" first -means to cause said first means to tend to follow a second rotary means movable about -a second axis between a circuit-closing position and a circuit-opening position, said second rotary means being mechanically responsive to said electrically controlled member to move to circuit-opening position when said member approaches said limit position` and,b to move to circuit-closingl position as said member initially retreats from said limit position; means responsive to said second rotary means to yieldingly urge said rst rotary means to follow the movements of said second rotary means; a rst latch means positioned on said first rotary means to be carried thereby in an arcuate path; and a second latch means positioned on said second rotary means to be carried thereby in an arcuate path across the arcuate path of said rst latch means, said second latch means being disposed and dimensioned to temporarily intercept and block said rst latch means to delay the movements of said first rotary means in both rotary directions.

3. A combination as set forth in claim 2 in which said first rotary means is in a first plane of rotation and said second rotary means is in a second plane of rotation spaced from the first plane, said nrst latch means projecting from the rst rotary means towards said second plane, and said second latch means projecting from said second rotary means towards said first plane.

4. Means for controlling a circuit at a limit position of a member controlled by the circuit,

' said means comprising: a switch in said circuit;

a switch operating member movable from a first position to a second position to open said switch and from said second position to said rst position to close the switch, said operating member being movable to said second position in response to approach of said controlled member to said limit position; yielding means operatively conn'ecting said operating member with said switch e; Vfor actuation of the switch; means operatively connected with said operating member to prevent actuation of the switch in opposition to said yielding means during initial movement of the operating member from said rst position to saidv second position and during initial movement of 'the operating member from said second position to said first position; and yielding means continuously urging said operating member toward said rst position to cause said operating member to moveto said first position automatically whenever saidicontrolled member departs from said limit position.

5. A limitl switch of the character set forth for controlling an electrically-controlled member at a limit position of the member, said switch comgprising: a pair of switch contacts; a rotary means movable in one direction about its axis to cause said contacts to separate and movable in the other direction to cause said contacts to close together; a second rotary means movable about a second axis between a circuit-closing position and acircuit-opening position, said second rotary lmeans being mechanically responsive to said electrically-controlled member to move to circuit-opening position whenever said member approaches said limit position; means responsive to said second rotary means to yieldingly urge said rst rotary means to follow the movements of said second rotary means; a first latch means positioned on said rst rotary means to be carried thereby in an arcuate path in opposite directions; a second latch means positioned on said second rotary means to be carried thereby in opposite directions in an arcuate path across the arcuate path of said rst latch means, said second latch means being disposed and dimensioned to intercept and block said first latch means during initial movement of said second rotary means froml said second circuit-closing -position and .duringlin-itial movement of said second rotaryV means from said circuit-opening position thereby to relay responsive movements of said rst rotary means in both directions; and yielding means urging said second rotary means to circuit-closing position to cause the second rotary means to move to said circuit-closing position whenever said electrically-controlled member initially retreats from said limit position.

6. A combination as set forth in claim in which said first rotary means is in a nrst plane of rotation, said second rotary means is in a second plane of rotation spaced from the first plane, said rst latch means projects from the first rotary means toward said second plane, and said second latch means projects from said second rotary means toward said rst plane.

7. A limitI switch of the character set forth for controlling an electrically-controlled member at a limit position of the member, said switch comprising: a pair 0f switch contacts; a movable member operatively connected with said pair of contacts, said movable member being-movable in one direction to cause said contacts to separate and in the opposite direction to cause the contacts to close together, said movable member having a rst face disposed toward one of its directions of movement and a second face disposed toward its other direction of movement; a switch-operating member movable between a circuit-closing position and a circuit-opening position, said switch-operating member being responsive to movement of said electrically-controlled member to and from said limit position; and yielding means operatively connecting said switch-operating member with said movable member to actuate the movable member, said switch-operating member having a rst retarding face position to extend across the path of said rsi-I face of the movable member during initial movement of the switch-operating member in one direction, said switch-operating member having a second retarding face positioned to extend across the path of the second face of the movable member during initial movement of the operating member in the opposite direction.

8. A limit switch of the character set forth for controlling an electrically-controlled member at a limit position of th'e member, said switch comprising: a pair of switch contacts; a rst rotary means movable in one direction about an axis to cause said contacts to separate and movable in the other direction to cause said contacts to close together; a second rotary means movable about a second axis between a circuit-closing position and a circuit-opening position, said second rotary means being mechanically responsive to said electrically-controlled member to move to circuit-opening position `whenever said member approaches said limit position and to move to circuit-cl-osing position as said member initially retreats from said limit position; yielding means interconnecting said two rotary means to be stressed by said second rotary means in one direction to cause said rst rotary means to move in one direction and to be stressed by said second rotary means in the opposite direction to cause said rst rotary means to move in the opposite direction; a latch means on said first rotary means directed toward saidY second rotary means; and a latch means on said second rotary means directed toward said first rotary means, said two latch means being positioned Vto follow intersecting paths, said second latch means having one face positioned to block said rst latch means during initial movement of said second rotary means in one direction, said second latch means having a second face positioned to, block said firstl latch means during initial movement of said second member in the opposite direction.

JAMES H. CANNON. 

